You can spray vinegar to kill aphids on contact, but you shouldn't. No university source backs this method at all. Vinegar burns your plant leaves just as fast as it kills the bugs. The damage you cause to your garden will be far worse than the aphids ever could have been. You have better options that cost the same and won't hurt your plants.
I tried a vinegar aphid spray on my pepper plants a few years back after reading about it online. I mixed one part white vinegar with three parts water and sprayed the leaves. The aphids on the surface died within hours. But by the next morning, every leaf I sprayed had turned brown at the edges and started to curl. I lost three healthy pepper plants trying to save them from a small bug problem that soap would have fixed in minutes.
The acetic acid in vinegar does kill soft-bodied insects on contact. That part is true. But it also eats through your plant's cell walls and strips the waxy layer that protects leaves from sun and disease. Pour enough on the soil and you'll shift the pH level in ways that hurt root health and kill helpful soil organisms. Garden Betty's myth-busting guide flags vinegar as a poor choice for this exact reason. Not a single Tier 1 university source backs it up as a safe or effective treatment.
You'll find a homemade aphid remedy vinegar mix all over the web because it's cheap and easy. That makes sense on the surface. You want something fast, free, and right at hand when you spot bugs on your plants. The problem is that cheaper doesn't mean better when the cheap option also kills the plant you're trying to protect. You wouldn't put bleach on a cut just because it kills germs.
A much better homemade option costs about the same and won't hurt your plants at all. Mix one tablespoon of pure liquid castile soap into one quart (about one liter) of water. Shake it up and spray it on the aphids. The soap breaks down the waxy coating on aphid bodies and causes them to dry out and die. Your plants stay green and healthy because castile soap is gentle on leaf tissue.
I switched to this soap mix after my vinegar mess and cleared a worse bug problem off my tomatoes in two rounds over ten days. The soap spray cost me less than a dollar to make and treated my entire veggie bed. My plants showed no stress at all after the treatment. That's the kind of result you want from a homemade remedy.
Apply your soap spray in the early morning or evening when the sun won't dry it too fast on your leaves. Coat the undersides of every leaf where aphids hide and feed. Repeat every 3-5 days until the colony is gone. You get the same contact kill as vinegar without the plant damage or burned leaves that come with acid sprays. Your garden will thank you for picking the smarter option.
A friend of mine tried apple cider vinegar on her rose bushes last year because someone on social media swore by it. Her roses lost half their leaves within days, and the aphids came back even worse on the fresh growth that followed. I helped her switch to the castile soap recipe and her bushes recovered in about three weeks. She hasn't touched vinegar for pest control since. Skip the vinegar and grab some castile soap instead. Your plants deserve a treatment that won't wreck what you've worked so hard to grow. You'll spend less than a dollar and get results that last.
Read the full article: Best Methods for Aphid Control
